An SMTP transaction is the handshake and commands used to deliver an email between servers. Understand the flow and why failures happen.
An SMTP transaction is the back-and-forth exchange between a sending server and a receiving server that transfers an email. It includes greetings, sender/recipient commands, and the data phase where the message is transmitted.
Many deliverability issues show up here: rejections, throttling, and temporary deferrals. Reading SMTP logs helps pinpoint whether the problem is authentication, reputation, content filtering, or recipient policy.